Extensible spring balance



28, 1951 A. DE VRIES ET AL 2,565,804

EXTENSIBLE SPRING BALANCE Filed Dec. 16, 1946 400/5 0 VP/[S BY PatentedAug. 28, 1951 UNITED STATES, PATENT OFFICE EXTENSIBLE SPRING BALANCEAbraham de Vries' and Louis de Vries, Amsterdam, Netherlands ApplicationDecember 16, 1946, Serial No. 716,520

and the like with spring balances 8 Claims. (Cl. 16-197) spiral stripmember having a gradually increasing pitch that is enclosed by a pair ofcoil springs, one of the springs acting as a torsion spring which exertsits reactive force on the spiral strip, and the other acting as atension or compression spring that is extended or compressed as the sashis raised or lowered.

Although spring balances of this type have been constructed wherein thenet effective force exerted by the balance remains substantiallyconstant in all positions, the amount of space made available in windowframes for the recep= tion of sash balances is so small as to require aselection of springs that are incapable of balancing heavier sash.

It has now been found that by using a spiral member having a reversetwist, the range of reaction forces exerted by a torsion spring and anextensible spring, such as a tension or compression spring, can beeffectively doubled, thus making it possible to increase greatly theload capacity without increasing the dimensions of the balance. g

One advantage of the balance of this invention, therefore, is that it iscapable of balancing objects such as window sash of greater weight thanwas hitherto possible with balances of equal dimensions.

This and other advantages, as well as the principles of the presentinvention will become more apparent from I the following detaileddescription made with reference to the accompanying drawing, it beingunderstood, however, that the invention is not limited to the particularconstruction illustrated or to the application thereof to the balancingof window sash.

In the drawing:

Figure 1 is a view in sectional elevation of a preferred embodiment ofthe invention as applied to a window sash; and

Figure 2 is a graphic representation showing the variation of forcesexerted by the spring within the balance while the balance is'ext'endedfrom its fully contracted position to its fully extended position.

In the embodiment illustrated by way of example in Figure 1, a windowsash'l is mounted slidably in a window frame 2. In a space between thesash I and the frame 2 there is posi- .The nipple the negatively slopingline ward reaction force of 30 the window sash I weighs 25 kilograms andthat extreme raised position may tioned a tension spring 3, one end ofwhich is attached to the sash by any suitable means at 4. The other endof the spring 3 is fixedly secured at 5 to a tube 6 which is in turnattached by means of a fastening member I to the frame A torsion spring9 within the tube 6 is fixedly connected to the tube at its upper end.The

lower end of the spring 9 is secured to a spiral engaging member whichmay be in the form of a nut or, as shown, in the form of a slottednipple ll] mounted for rotation in the 'tube 6. Hi, at point ll, engageswith a spiral member which may be in' the form of a screw threaded baror, as shown, in the form of a spiral strip l2. The spiral strip [2 issecured to the spring 3 at l3 and reverses its pitch at M.

The operation of the spring balance illustrated in Figure l incounterbalancing window sash will now be explained with reference toFigure 2,

wherein the ordinate axis o-y indicates force in kilograms exerted in anupwardly direction,

the abscissa o-.r represents the amount of movement of the sash in adownwardly direction, the positively sloping line represents the upwardreaction force of the tension spring 3 and represents the upthe torsionspring 9.

Assuming, for the purpose of illustration, that only one spring balanceis to be employed to counterbalance it, the tension spring, in itscontracted position, i. e., when the sash is in its be biased to exertan upward reaction force of 15 kilograms onthe sash at 4. At this pointthe nipple ill engages the spiral strip l2 near its lower end, at whichthe strip has its minimum positive pitch. The

torsion spring 9 is biased to exert a torque or rotational force on thenipple, i. e., it tends to unwind in a clockwise direction when viewedfrom above. The pitch of the spiral strip l2 at its lower end and thebias of the torsion spring 8 is such that the vertical component of thereaction force exerted by the nipple ill on the spiral strip and,therefore, the sash l, is 10 kilograms in an upwardly direction. Thetotal effective force exerted by the springs 3 and 9 is therefore 25kilograms. the weight of the sash.

As the sash is lowered toward its half -way position, represented inFigure 2 by X1, the tension spring 2- is stretched and therefore exertsa gradually increasing force in the upwardly di rection until it becomes25 kilograms at X1. At the same time, the spiral strip [2 movesoutwardly I the algebraic sum of the tube 6 and the torsion spring 9 iswound up. Due to the gradual increase in pitch of the spiral, thevertical component of the reaction force exerted by the nipple on thespiral strip l2 gradually diminishes notwithstanding the fact that thetorsion spring 9 is wound up until it becomes zero when the nippleengages the strip at point l4 since the pitch at that point is 90. Hereagain the total efiective force exerted by the springs 3 and 9 is,therefore, 25 kilograms.

When the sash is further lowered. to its lowermost position, asillustrated in Figure 1, the tension spring 3 is further stretched untilit exerts a maximum force, in an upwardly direction, of 35 kilograms. Atthe same time, the spiral strip l2 moves outwardly of tube 6 and thetorsion spring 9 is unwound. Due to the gradually decreasing negativepitch of the spiral engaged by the nipple ID, the torsion spring 9,through the medium of the nipple exerts a gradually increasing force,notwithstanding the fact that the torsion spring is unwound further allthe time, in a downwardly direction on the spiral strip until it becomes10 kilograms at position X11. Thus of reaction forces of the springbalance is again 25 kilograms in an upwardly direction.

From th foregoing description, it is evident that the total effectiveforce exerted in an up- Wardly direction by the sprine balance remainssubstantially constant at all positions of the sash. Furthermore, theefiective ranges of reaction forces exerted by the springs are, due tothe reverse twist in the spiral strip 32, twice as great as they wouldbe if the spiral strip were twisted in only one direction.

It is to be understood that the tension spring 3 may be replaced by a,compression spring and that innumerable other changes and modification,which will become apparent to those skilled in the art upon reading theforegoing description, may be made without departing from the principlesof this invention as defined in the appended claims;

We claim:

. 1. An extensible spring balance comprising a reversely twisted spiralmember securable at one end against rotation, an extensible springmember having a first and second end surroui1ding said spiral member,the first end of said spring member being movable With the securable endof said spiral member and the second end of said spring member beingmovable relative to said first end, a spiral engaging member within saideX- tensible spring member and rotatable on said spiral member uponmovement along the length thereof, and a torsion spring member withinsaid extensible spring member, one end of said torsion spring memberbeing secured within and immovable relative to said second end of theextensible spring member and the other end of said torsion spring memberbeing fixed to said spiral engaging member, said spiral member, spiralengaging member, extensible spring member and torsion spring membercooperating to exert a substantially uniform force between the securableend of the spiral member and the second end of said extensible springmember while said extensible spring member is in various degreesofextension.

2. An extensible spring balance comprising a reversely twisted spiralmember securable at one end against rotation, a tension spring memberhaving a first and second end and surrounding said spiral member, thefirst end of said spring member being movable with the securable end ofsaid spiral member and. the second end of said spring member beingmovable toward and away from said first end, a nipple within saidtension spring member, said nipple engaging with said spiral member andbeing rotatable thereon upon movement along the length thereof, and atorsion spring member within said tension spring member, one end of saidtorsion spring member being secured within and immovable relative tosaid second end of the tension spring member and the other end of saidtorsion spring member being fixed to said nipple, said spiral member,nipple, tension spring member and torsion spring member cooperating toexert a, substantially uniform force between the securable end of thespiral member and said second end of said tension spring member whilesaid tension spring member is in various degrees of extension.

3. An extensible spring balance comprising a spiral member securable atone end against rotation, said spiral member being twisted in onedirection between its midpoint and one end and in the opposite directionbetween its midpoint and the other end, an extensible spring memberhaving a first and second end and surrounding said spiral member, thefirst end of said spring member being movable with the securable end ofsaid spiral member and the second end of said spring member beingmovable relative to said first end, a nipple within said extensiblespring member, said nipple engaging with said spiral member and beingrotatable thereon upon movement along the length thereof, and a, torsionspring member within said extensible spring member, one end of saidtorsion spring member being secured within and immovable relative tosaid second end of the extensible spring member and the other end ofsaid torsion spring member being fixed to said nipple, said spiralmember, nipple, extensible spring member and torsion spring membercooperating to exert a substantially uniform force between the securableend of the spiral member and said second end of said extensible springmember while said extensible spring member is in various degrees ofextension.

4. An extensible spring balance comprising a spiral member securable atone end against rotation, said spiral member being twisted in onedirection between its midpoint and one end and in the opposite directionbetween its midpoint and the other end to form convolutions havinggradually decreasing pitches as they approach the ends of the spiralmembers, an extensible spring member having a first and second end andsurrounding said spiral member, the first end of said spring memberbeing movable with the securable end of said spiral member and thesecond end of said spring member being movable relative to said firstend, a nipple within said extensible spring member, said nipple engagingwith said spiral member and being rotatable thereon upon movement alongthe length thereof, and a torsion spring member within said extensiblespring member, one end of said torsion spring member being securedwithin and immovable relative to said second end of the extensiblespring member and the other end of said torsion spring member beingfixed to said nipple, said spiral member, nipple, extensible springmember and torsion spring member cooperating to exert a substantiallyuniform force between the securable end of the spiral member and saidsecond end of said extensible spring member while said extensible springmember is in various degrees of extension.

5. A sash balance for a window comprising an extensible spring member,one end of said spring member being secured to the window sash and theother end being secured to the window frame, a reversely twisted spiralmember within said spring member, one end of said spiral member beingsecured against rotation to one end of said spring member, a spiralengaging member within said extensible spring member and rotatable onsaid spiral member upon movement along the length thereof, and a torsionspring member within said extensible spring member, one end of saidtorsion spring member being secured within and immovable relative to theend of the extensible spring member remote from the end to which thespiral member is secured and the other end of said torsion spring memberbeing fixed to said spiral engaging member, said spiral member, spiralengaging member, extensible spring member and torsion spring membercooperating to exert a substantially uniform force to counterbalance theweight of the window sash in all positions thereof relative to thewindow frame.

6. In an extensible spring balance having a spiral member and a coilspring cooperatively engaged to exert a substantially uniform forcewhile the balance is in various degrees of extension, one portion ofsaid spiral member being twisted in clockwise direction and anotherportion thereof being twisted in counterclockwise dimotion 7. In anextensible spring balance having a spiral member and a coil springcooperatively engaged to exert a substantially uniform force while thebalance is in various degrees of extension, said spiral membercomprising an elongated strip having parallel sides, said strip having atwist in one direction from the mid-point thereof to one end and a twistin the opposite direction from the mid-point to the other end.

8i In an extensible spring balance having a spiral member and a coilspring cooperatively engaged to exert a substantially uniform forcewhile the balance is in various degrees of extension, said spiral membercomprising an elongated strip having parallel sides, said strip having atwist in one direction from the mid-point thereof to one end and a twistin the opposite direction from the mid-point to the other end, thenumber of turns per unit length of said strip increasing graduallytoward both ends.

ABRAHAM DE VRIES. LOUIS DE VRIES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'IDENTS Floreth Mar. 14, 1939

